Microfluidics systems are miniaturized systems wherein chemical, biochemical, or biological reactions occur. Microfluidics can also be used in analytical systems. Microfluidics are used due to, but are not limited to, integration with several functionalities, integrated to one system, portability, short time to result, and economical use of samples and reagents.
The flow regime of liquids in microfluidics is generally laminar, turbulence phenomena are absent and diffusion of species in liquids (analytes, reactants, etc.) is passive. For example, two parallel liquids that enter a same microchannel do not mix well and their flows essentially remain separate parallel streams. The lack of mixing or an inefficient mixing in microfluidics is therefore a commonly encountered problem.
Mixing is usually implemented using actuated elements that physically move and change the flow path of liquids to make their flow less laminar. This adds to the complexity and cost of the fabrication and use of microfluidic systems. Mixing is sometimes performed using passive mixers.
Passive mixers are usually microstructures (e.g. curved or otherwise shaped microchannels) that modify the direction of flow of streams of liquid or that enhance the interface (contact area) between adjacent streams of liquid (e.g. flow splitters). Some passive mixers induce chaotic, turbulent flow in liquids. However, these mixers have characteristics defined by design and cannot be modified during usage of the microfluidics.
Particles have been used to stir liquids and generate mixing but this requires continuous actuation for moving the particles in a region of a microfluidic. For example, magnetic particles are rotated using a magnetic field or charged particles are moved using an electrical field.